This invention relates to the formation of continuous glass strands. More particularly, the present invention relates to an applicator for metering sizing onto continuous glass filaments prior to their collection into strands.
A typical strand formation technique is shown in U.S. Pat. No. 3,414,956. Glass filaments are drawn from a tipped bushing, a sizing is applied, the filaments are collected into a plurality of multi-filament strands and then the strands can be (1) wound onto a collection drum as shown in the patent or, (2) pulled and chopped into short segments for use in reinforcing various materials including concrete, paper, glass mat and plastics. The sizing performs an important function: it prevents the filaments from abrading each other due to frictional rubbing in the strands. Such abrasion can reduce the tensile strength of the strands by 50% or more.
Many types of sizing applicators have been developed. The key drawback of most, is that they require rather close watching and adjustment to insure adequate amounts of sizing are applied without unnecessary waste. Some applicators have no adjustment capability and hence are designed to over apply. Because the operators are occupied making sure the filaments are being attenuated properly, they seldom make the necessary adjustments to the applicators that do have such adjustability. To avoid scrapping the production material as a result of too little sizing (which will become apparent from tensile strength tests), most operators will set these sizing applicators for their maximum rate of application, with significant sizing being wasted. Further, the excess sizing results in wetter fiber requiring drainage and drying.
The applicator of the present invention overcomes these difficulties. Its design makes it less susceptible to operational variations. Accordingly, once the applicator has been properly adjusted, little or no further adjustment is necessary. In addition, the applicator of the present invention permits a large range of "proper" adjustments. Therefore, an adequate amount of sizing is applied without resorting to excessive application and waste, producing a dryer fiber.
The sizing applicator of the present invention comprises an applicator roll rotated in the direction of movement of the glass strands at a variable speed, a resilient dispensing means in contact with the applicator roll for metering the sizing thereupon, the combination of the pressure exerted by the dispensing means on the applicator roll and the rate of rotation of the applicator roll controlling the amount of sizing that is applied to the moving glass strands.
In one embodiment of the present invention, the dispensing means comprises a second roller which is covered with a foam or sponge layer. This roller is rotated in the same rotational direction as the applicator roll and the rate of rotation of the applicator roll and pressure exerted by the foam-covered dispensing roller on the applicator roll, determine the size of a puddle of sizing formed in the nip between the roller and the roll which, in turn, determines the amount of sizing applied.
In an alternative embodiment, the resilient dispensing means is a generally rectangular reservoir of urethane or the like, which sits generally atop the applicator roll. The surface which contacts the applicator has a plurality of metering slots therein. By adjusting the pressure exerted by the reservoir on the applicator roll, the width of the slots and the amount of sizing exiting therefrom can be controlled.
In both embodiments, excess sizing is pumped through a closed loop in order that the temperature and viscosity of the fluid may be more closely controlled. This enables the amount of sizing applied to the glass to be more closely metered than would otherwise be possible.
Other features, advantages and characteristics of the present invention will become apparent after a reading of the following specification in conjunction with the accompanying drawings.